Automatic receiver gain control circuits



May 3, 1938 H. PITSCH 2,115,871

AUTOMATIC RECEIVER GAIN CONTROL CIRCUITS Filed Oct. 9, 1936 2 Sheets-Sheet 1 70L. j SIGNAL 3:- SOURCE 70.. E SIGNAL 5 some;

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lNV ENTOR HELMUT PITSCH ATTORNEY May 3, 1938. H, PTSCH 2,115,871

AUTOMATIC RECEIVER GAIN CONTROL CIRCUITS Filed Oct. 9, 1936 2 Sheets-Sheet 2 70 z E E SIG/VAL 3- SOURCE 3 A i *G.

l 1 -G MAX.

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INVENTOR HELMUT PITSCH BY )QZMW ATTORNEY Patented May 3, 1938 UNITED STATES PATENT OFFICE CIRCUITS AUTOMATIC RECEIVER GAIN CONTROL Germany Application October 9, 1936, Serial No. 104,768 In Germany October 18, 1935 9 Claims.

Receivers comprising means adapted to insure automatic volume control offer the practical advantage that all transmitter stations come in approximately with like intensity, and that the effects of fading are neutralized. However, there is the disadvantage that the various stations are not audible the loudest at a single or definite point, but that they come in with undiminished power or strength also at points adjacent the tuning point since the receiver tends to raise the in those regions adjoining the tuning points. However, inasmuch as reception in the presence of inaccurate tuning is distorted because of the cutting off of portions of the side-bands and reduction of the strength of the carrier frequency compared with the side-bands, optical indicator means are provided in receivers designed for automatic volume control by the aid of which the proper point of tuner setting is made known.

Now, attempts have been made to render such an accessory device dispensable by suggestions to build the receiver in such a way that the receiver apparatus needs to be set or tuned only proximately, while automatic means become operative which will efiect readjustment to the proper value or point. However, arrangements of the said kind require considerable expenditure of money and materials. It is known in the prior art to couple the tube serving to eliminate cracking noises (insure silent tuning) by way of a sharply tuned or highly selective circuit, the said tube blocking the reception whenever unduly small radio frequency amplitudes are coming in; the result is that in this manner strays and noises which become thus audible between the stations, and which are specially emphasized because of the volume control, will be suppressed. What is meant by the said highly selective circuit is a simple tuning circuit rather than a band-pass filter. In this manner, reception upon tuning is rendered operative, or is released, later than would he the case in the absence of such a coupling. l/Vhat is worse is that reception is not yet permitted or insured at a sharply defined and optimum point, so that the further suggestion has been made in the earlier art to couple an oscillating tube with the rectifier serving to suppress noise, the said tube serving to suddenly diminish the suppression potential whenever the incoming signal oscillation entrains the locallygenerated oscillation inside a small range (or pulls the same into step). Such a circuit arrangement is quite complicated, and is not adapted to a simple regulation.

According to this invention automatic sharptuning is secured by that the'loosely coupled oscillatory circuit with which the rectifier intended to suppress cracking noises is connected, is endowed with a more pointed or peaked resonance curve by. the aid of regeneration. What is here meant by sharp tuning accomplished automatically is that the operator, oruser, of the set need not pay any particularly close attention to exact tuning. While normally enhanced selectance of reception is achievable by resorting to regeneration, the ways and means here disclosed operate in such a way that the transmitter station appears only at one definite sharply and narrowly bounded place so that optical indicator, or marking, means become dispensable. The quality of reception is not impaired by resorting to regeneration, on the contrary, it is even improved seeing that erroneous tuning is precluded.

A number of exemplified embodiments of the idea underlying this invention are shown in the drawings. Figs. 1 to 4 inclusive show difierent modifications of the invention. The circuits show intermediate-frequency (beat) receivers, though the invention by no means is confined to the application in receivers of the said type. In T. R. F. receivers, to be sure, there arises the disadvantage that the loosely coupled oscillation circuit must also be tuned to the desired transmitter station.

Referring to Fig. 1, the intermediate-frequency current flows from the oscillatory circuit Z, on the one hand, to the rectifier G of the receiver with resistance W1; and, on the other hand, by way of the small condenser C (loose coupling) to the oscillation circuit S. In the presence of sharp tuning to a certain station, a negative biasing voltage arises across the resistance W2 by rectification between the grid and the filament of tube K so that the blocking voltage for the audio amplifier tube N prevailing in quiescent state across the resistance W3 is discontinued. The tube R is fed with radio frequency energy directly from the oscillation circuit S, and by the aid of the tickler (regeneration) coil RK a feedback action is produced in the oscillation circuit S. With tube K regeneration isnot possible inasmuch as this tube is blocked when tuning to a transmitter station. Another exemplified embodiment is il lustrated in Fig. 2, which offers the special advantage that the plate current of the'blocked audio tube will not counteract the arising of an unblocking potential across resistance W3. In Fig. 2, when blocking the tube K, there occurs a shift of point P in a positive direction so that tube N, by way of resistance W3, is impressed with fed with a high plate potential in order that upon the arising of a negative potential across theresistance We the left-hand tube system will not yet be blocked so that, if possible, no change in the slope or mutual conductance occurs as a result of the shift of the working point. The plate potential for the plate 2 of the right-hand system, on the contrary, is so proportioned'that blocking will be produced. This plate potential which arises between G and Gmax is low alone by reason of the requisite small blocking potential.

In the case of the scheme in Fig. 4, recourse is had to a pentode K1. The first grid 3 and the screen grid t serve for the production of the feedback current, while the third grid 5 and the plate 6 properly so-called are employed for in suring the blocking and unblocking actions. Since, when tuning to a transmitter station, a negative biasing voltage is set up across the resistance We, the stream of electrons will be forced more strongly on the screen grid. Thereby the feed-back is raised with the result that in tuned state the resonance curve is automatically rendered still sharper.

What I claim is:

1. In combination with a signal transmission tube, means normally operative to block signal transmission through said tube, a highly selective tuned signal input circuit connected to said blocking means, means in saidinput circuit for rendering the blocking means inoperative when signals of the frequency of said input circuit are impressed on the latter, and means, responsive to said signals, for regeneratively feeding back signals to said input circuit thereby to increase the selectivity of the latter to a substantially greater degree.

2. In combination with a signal transmission tube, means normally operative to block signal transmission through said tube, a highly selective tuned signal input circuitconnected to said blocking means, means in said input circuit for rendering the blocking means inoperative when signals of the frequency of said input circuit are impressed on the latter, means, responsive to said signals, for regeneratively feeding back signals to said input circuit thereby to increase the selectivity of the latter to a substantially greater degree, and said feedback means comprising a tube which is independent of said blocking means.

3. In combination with a signal transmission tube, means normally operative to block signal transmission through said tube, a highly selective tuned signalinput circuit connected to said blocking means, means in said input circuit for rendering the blocking means inoperative when signals of the frequency of said input circuit are impressed on the latter, means, responsive to said signals, for regeneratively feeding back signals to said input circuit thereby to increase the selectivity of the latter to a substantially greater degree, said blocking means comprising a tube, and said feedback means including a second tube independent of said blocking tube.

4. In combination with a signal transmission tube, means normally operative to block signal transmission through said tube, a highly selective tuned signal input circuit connected to said blocking means, means in said input circuit for rendering the blocking means inoperative when signals of the frequency of said input circuit are impressed on the latter, and means, responsive to said signals, for regeneratively feeding back signals to said input circuit thereby to increase the selectivity of the latter to a substantially greater degree, said blocking means including a tube provided with a cathode, control grid, plate and one auxiliaryelectrode, said auxiliary electrode being regeneratively coupled to said selective input circuit to provide said feedback means.

5. In combination with a signal transmission tube, means normally operative to block signal transmission through said tube, a highly selective tuned signal input circuit connected to said blocking means, means in said input circuit for rendering the blocking means inoperative when signals of the frequency of said input circuit are impressed on the latter, and means, responsive to said signals, for regeneratively feeding back signals to said input circuit thereby to increase the selectivity of the latter to a substantially greater degree, a signal source coupled to said input circuit, a demodulator'coupled to said source, the input electrodes of the transmission tube being coupled to the demodulator.

6. In combination with a signal transmission tube, means normally operative to block signal transmission throughsaid tube, a highly selective tuned signal input circuit connected to said blocking means, means in said input circuit for rendering the blocking means inoperative when signals of the frequencyof said input-circuit are impressed on the latter, means, responsive to said signals, for regeneratively feeding back signals to said input circuit thereby to increase the selectivity of the latter to a substantially greater degree, a demodulator coupled to said signal transmission tube, and means responsive to signal amplitude increase for maintaining the signal amplitude at the demodulator input substantially uniform.

'7. In combination with a signal transmission tube, means normally operative to block signal transmission through said tube, a highly selective tuned signal input circuit-connected to said blocking means, means in said input circuit for rendering the blocking means inoperative when signals of the frequency of said input circuit are impressed on the latter, means, responsive to said signals, for regeneratively feeding back signals to said input circuit thereby to increase the selectivity of the latter to a substantially greater degree, a signal source coupled relatively loosely to said input circuit, a signal detector coupled to said source'and providing audio and direct current voltage, means for impressing the audio voltage on said transmission tube, and automatic volume control means utilizing said direct current voltage.

8. In combination with the intermediate frequency network of superheterodyne receiver, means demodulating the intermediate frequency energy, means for amplifying the demodulated energy, a tube having its space current path arranged to'provide a normal blocking bias for the amplifying means, said tube having an input circuit tuned to the intermediate frequency, means for impressing intermediate frequency energy on said input circuit, means responsive to intermediate frequency energy in said input circuit for reducing said space current to an extent such that said bias is removed, and means including an electron discharge device, responsive to intermediate frequency energy in said input circuit, for providing regenerative feedback of the intermediate energy to said input circuit thereby greatly to increase its selectivity.

9. In combination with the intermediate frequency network of superheterodyne receiver, means demodulating the intermediate frequency energy, means for amplifying the demodulated energy, a tube having its space current path arranged to provide a normal blocking bias for the amplifying means, said tube having an input circuit tuned to the intermediate frequency,

means for impressing intermediate frequency energy on said input circuit, means responsive to intermediate frequency energy in said input circuit for reducing said space current to an extent such that said bias, is removed, and means including an electron discharge device, responsive to intermediate frequency energy in said input circuit, for providing regenerative feedback of the intermediate energy to said input circuit thereby greatly to increase its selectivity, said device including at least one electrode in said blocking tube which is auxiliary to the normal electrodes thereof.

HELMUT PITSCH. 

